Telephone transmitter



Feb. 27, 1940.y E. S. MQLARN TELEPHONE TRANSMITTER Fill'd Ilarh 31, 1937 4 SheIetS-Sheet l INVENTOR ERNEST f NCL/48N ATTORNEY Feb.' 27, 1940. E. s. McLARN TELEPHONE TRANSMITTER Filed umn s1. 19:57

4 sheets-Sheet '2 L i wk.; n?

Feb, 27, 1940.

E. S. MGLARN TELEPHONE TRANSMITTER Y Filed March 3l, 1937 4 Sheets-Sheet 5 \g.w/ Y 8 INVENTOR ERA/E67' 5. Mel/MW:

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ATTORNEY Feb. 27, 1940.

E.S.MLARN v TELEPHONE TRANSMITTER Filed March 3l. 1937 4 Sheets-Sheet 4 ATTORNEY Patented Feb. 2?, ld@

PATENT orifice TELEPHONE TRANSMITTER Ernest S. McLarn, Manhasset, N. Y., assigner to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application March 31, 1937, Serial No. 134,044

' 9 Claims.

`This invention relates to telephone apparatus and pertains more particularly to telephone transmitters.-

It is an object of my invention to provide an 5 improved `iorzn `of variable resistance element,

which is moisture proof and resistant to atmospheric changes.

More specifically, it is an object of my invention to provide an improved form of telephone transmitter wherein the carbon granules or other resistance elements are enclosed in a moisture proof housing. l

A still further 'object of my invention is to provide a variable resistance element which is especially adapted -ior use in a telephone transmitter, which element is compact, .simple in construction and low in cost.

Another object of my invention is to provide a telephone transmitter variable resistance element which hasv a relatively high heat dissipating capacity and therefore a high current carrying ability. i

Telephone transmitters constructed in accordance with `the teachings of the prior art, for exampie, those utilizing a silk bag for holding the carbon granules, have at times given a considerable amountof trouble due tomoisture precipi-l tated on the active parts thereof duringparticularly humid weather. This effect has been en- 30 countered to a certain extent in the tropics, for

example. A further disadvantage has been that certain of the metal parts of the transmitter have been subject to atmospheric corrosion and electrolytic action. which has interfered with the eHective operation thereof and limited the life of the instrument.

In accordance with my invention Ythe carbon,

lows in liquid varnishand subsequently subject-l ing it to a drying operation before the carbon "granules are inserted. Other insulatingmaterial might be provided inside the bellows since moisture and sir are excluded therefrom'. The

silk material formerly used for making the carbon bag or chamber might be'used for this insulation, either by itself or in'cooperation'with a layer of insulating varnish such as already described.

The metal bellows is -preferably of brass or less elastic, for example, silk. The metal bellows lo" being substantially in contact with the carbon granules serves readily to conduct the heat therefrom, whereby a greater amount of current can I be' passed through the transmitter button or variabie resistance than would be the case if the 15 carbon material were enclosed in an insulating chamber which would have a poorer heat conductivity than the metal of which lthe bellows is formed. l

The above mentioned and further objects and 2 advantages of my invention and the manner of attaining them'will be more fully explained in the followingv description taken in conjunction with the accompanying drawings.

In the drawings, Fig. 1' shows in side elevation 25 y Y and partly in section a telephone transmitter assembly constructed in accordance with my invention; Fig. 2 shows a modified iormof coni struction using a slightly different shape of metal bellows; Fig. 3 illustrates another modication 30 wherein a different type of seal is utilized; Figs.

4, 5, 6 illustrate still further embodiments of my' invention; Figs. 'l and 8 illustrate in side eleva-u tion a closure for the transmitter unit; and Fig. 9 illustrates in side elevation and partly in section 35 yet another embodiment of my invention.

Referring more particularly to the drawings, reference numeral I indicates a 'telephone transmitter housingv of any suitable insulating material having ilxed'thereto, for example by a mold- 40 ing in process, metal rings 2 and 3. which are v held in spaced relation by spacing posts 4 which interconnect the rings electrically. Centrally disposed with respect to the rings 2 and I and insulated therefrom, is a metal nut insert i. 45 whichlserves to hold the transmitter button assembly or variable element 6 in position. The

transmitter button comprises a metal bellows "l, which may be of brass, aluminum or the like, of

a springy nature and a thickness of a few thou- 5o sandths of an inch, e. g. approximating that of writing paper, this bellows being coated4 on the inside with insulating varnish enamel or similar insulating material as indicated by reference numeral 8. v"l'he side walls of the bellows are made 55 reentrant at the lower end thereof, thereby providing an end closure, this end closure being apertured at the center thereof. A back electrode or pressureelement 9 is positioned inside of the bellows l, element having a threaded shank Iim I0 which passes loosely through thev aperture II of the chamber, not touching the edges thereof, this pressure element being insulated from the bellows by means of washers I2 of mica or otherinsulating material. The entire pressure element is held against movement by means of nut I3 threaded on the shank I0, the latter being in turn screw threaded into the nut 5, which is molded into the housing I, thereby bringing the bellows into direct contact and electrical connection with the metal rings 2 and 3. The ring 2 with the nut 5 serve as terminals whereby electrical connec tion can be made with the transmitter unit.

The interior of the metal bellows or carbon chamber 1 is filled with a mass of granulated carbon AI4 and the upper end of the bellows is closed by means of a cap I5 which is crimped and/or soldered to the upper edge of the bellows 1. This cap has an indented center portion which acts as a front electrode or second pressure element thereby serving, upon the application of pressure to the end plate, to compress the carbon granules between the end plate and the back electrode 9, this compression causing a variation in resistance and a desired control of the current passing through the device. Reference numeral I6 indicates a corrugated diaphragm of anodic aluminum, duralumin or other light, springy material such as Bakelized silk which is supported at its periphery between two washers of phenol bre or other similar ma terial indicated by I1. These washers are compressed so as to hold the diaphragm in position, by means of a perforated closure or cap I8 which is crimped or otherwise fastened to the housing I at I9. The arrangement of parts is such that the diaphragm normally presses lightly against the cover I5 of the bellows, preferably being electrically insulated therefrom by means of a washer 20 of mica, phenol fibre or other suitable insulating material. Reference numeral 42 indicates a seal of high melting point wax or other suitable material which serves further to prevent access of air and moisture to the inside of the bellows.

From the foregoing description it will be seen that the carbon granules inside of the element 6 are prevented from contact with the air and from the deleterious effects of moisture by the screw connection and washer I2, and the wax seal 42 at the base thereof and by means of the soldered cover I5 at the top thereof. At the same time electrolysis and resulting corrosion of the transmitter diaphragm I6 is eliminated by insulating this Aelement from the top of the bellows 1 through use of the insulating washer 20, the outer edge of the diaphragm being, at the same time, free from connection with metal parts.

Fig. 2 illustrates a somewhat similar construction lwith the exception that the metal bellows has the upper portion 2| formed integrally with the side 22 thereof, the nal closure or cover 23 being at the bottom thereof, the connection between the two parts being by means of soldering or welding. In this modification the bellows has been shown as barrel shaped instead of corrugated as in Fig. 1, but the method of forming the top and bottom closures may be the same as that used with other shapes of bellows.

Fig. 3 illustrates a still further embodiment of my invention wherein the carbon chamber comprises a side wall 24 of cylindrical shape closed at the top by means of a ap 25 and having integrally formed with the lower end thereof a ex.-

,the carbon granules.

ible corrugated diaphragm portion 26 having a central aperture 21 therein. Positioned in the aperture just mentioned and surrounding post 28 of back electrode 29 is a bead of glass or other insulating material 30. which serves hermetically to seal the carbon container. In case that a glass bead is used at this point a satisfactory seal may be formed by welding or fusing the glass to the diaphragm and to the post 28 in air tight fashion in accordance with the teachings of the vacuum tube and electric light art. Under the back electrode 29 is a mica washer 3I which supports Suitable means such as a second washer of phenol fiber or other suitable material 32.8 provided to hold the mica washer in position, the second mentioned washer 32 being held in position by a friction grip with the post 28, preferably being a drive fit therefor. The post 28 is soldered or riveted into a bushing 33 molded in the housing I thereby making a first connection, while the second connection, that is, the connection to the diaphragm .26, is made by means of a wire 34 electrically connected to a second bushing 36 molded in the housing I. While this welded glass seal is shown in connection with a straight side bellows having a dexiblev diaphragm at the bottom thereof, the seal may also be used with other typesof bellows, such for example as shown in the other figures of the drawings.

The structure of Fig. 4 is somewhat similar to that of Fig. 3, except that the center post 28 is screw threaded to a nut 31 imbedded in the housing I and that the carbon chamber 24 ls contacted at its lower end directly with two rings 38 and 39 molded in the housing I, these rings being spaced by members 40 which connect the rings electrically, and being insulated from the nut 31 in substantially the same way as described in connection with Fig. 1. In this device the flexibility of the unit is secured by means of a corrugation 4I placed in the side walls of the container 24. Seals of high melting point wax or the like are provided at points 42 and 43.

In Fig. 5 the construction of the housing and metallic insert is the same as in Fig. 1, the olii.'u ference in the structure residing principally in the manner of securing the metal bellows to the housing. In this case the metal bellows has at its lower end an inwardly turned flange 44 resting on the conducting ring 3. A washer of phenol fiber or other insulating material 45 is positicned between the pressure element 9 and the inwardly turned flange, the screw threaded con- Y nection between post I0 and nut 5 serving to hold the entire assembly in rigid position. Reference numeral 42 indicates a wax seal similar to that shown in Fig. 1, for the purpose of preventing the -entrance of moisture. In this figure an alternative form of arrangement with respect to the transmitter diaphragm is shown. The diaphragm has a central aperture at 45', through which a screw threaded projection 46 of the cap I5 projects, the diaphragm being firmly xed to the element I5 by means of a nut of phenol fiber or other insulating material 41. A washer 48 is furnished to insulate the diaphragm I6 from the element I5.

In Fig. 6 the construction of the housing 5I! is somewhat different from that of the other figures, being of metal. This housing has an aperture at the lower side thereof through which passes a post or shank 5I, the upper end of which forms a back electrode 52. Between the back electrodo portion and the shank is a shoulder Il errer o. iront e 'a dat electrode likewise being suitable.

This upper electrode is formed. of thin metal pressed to the desired shape has in it a olurality ci small holes t3 having a diameter o bout .di inch or less. soldered to the upper side of the iro-nt electrode is a second bellows dfi which is very much weaker than the bellows t@ so that when any expansion of air or other gas inside of the space enclosed by the bellows takes place, the upper small bellows Gt instead of the main bellows will expand to taire care of the increased pressure whereby any appreciable displacement between the front and back electrodes 6i and 52, respectively, is prevented from' occurring. In place of the upper small bellows il an expansion chamber of vulcanized neoprene, natural rubber or the like, may be provided. For example, a discof this material may be cemented or clamped to the upper side of the front electrode 6I thereby forming a closure which will bulge outwardlyas the pressure within the main bellows increases with a rise in temperature. Such a rise in temperature might result from prolonged operation of the transmitter or from its use in an atmosphere subject to wide temperature changes.

In place of a solid front electrode 6| pierced by.

a plurality of small holes, a wire mesh electrode might be used, the mesh being one hundred or finer, for example, such a mesh screen might be of brass, gold plated. 'Ihe other electrodes described in the present application might also begold plated although it may be found possible in certain cases to omit this gold plated joint formed by the vconstruction described. Alternatively the surfaces of the electrodes may be of polished carbon. This will be particularly true in case a relatively inert gas, such as nitrogen or the like is used inside of the bellows. Ob-

viously in Fig. 6, as in the other figures, the l space inside of the bellows is filled with granular carbon. t

In Flg. 6 the closure or cap I8 is of a collapsible type adapted for easy removal and replacement, as will be explained more fully in connection with Figs;y '1 and v8. This cap has near its outer edge an indented ring 65 which is adapted to engage the outer edge of the diaphragm I8, no gaskets being provided. The diaphragm is'apertured at the center portionlto engage the bellows 56 and at the same time provide an opening for the auxiliary bellows or expansion chamber 64. The cap when placed in position engages the outer edge of the diaphragm and places it under a slight bending force which causes the diaphragm firmly to engage the top of the bellows 58. This type of construction has been found to lessen distortion of the diaphragm and as a result improve the quality of transmispreferably insulated on the upper surface thereof by means of a coat of varnish enamel or by sion oi sound. ihis method of holding the diaphragm is not limited to the structure shown in Fig. 6 but may be used with other structures, for example, as shown in the preeeding heures.

En Figs. l 8 the ciosure or eapi@ is of the collapsible type having a harige Et which is divided inte e. plurality of sections or ngers lil, which serre normally the vsides ci? housing i, as shown El, for example. By pressing on the end of the can the fingers are apar. shown in El, in which condition the can be placed on or removed from the housing. f le resilient sauce ig action oi the fingers wl-ren. in position causes the diaphragm lite be held firmly and resiliently against bellows as shown in d er between the eorlr washers il as illus' ed in i, and thereby prevents the diep agar from becoming loose. Furthermore, the can be quickly and easily removed without tools for inspection and repairs.

Fig. 9 illustrates transmitter somewhat similar to that of Fig. d. The variable resistance unit has a slightly' different construction that the 'upper portionl is dooie shaped, forming the front electrode. The back electrode 1i is of e. roughly similar shape and has a shankv 12, either screw threaded thereto as shown, or integral'therewith, and the shank is .sealed by glass bead it to a disc 14 of copper or other suitable material, in the same manner as in the structure of Fig. 6. The metal bellows 15 is crimped or soldered, or both, to the edge of the disc 14, preferably so as to form an air tight seal.

The self-contained resistance unit above described is centered with respect-to the housing 50 by means of a ring 15 embossed in the housing, this ring just tting Within the end 16 of the metal bellows, the whole resistance vunit being held imposition by nut 11 on the screw threaded portion of the shank 12.v This nut .presses against a metal washer 18. and insulating washer 19 thereby drawing the copper disc 14 and attached metal bellows down against the embossed ring 15. A shoulder on the shank 12 prevents too great strain being placed on the copper disc and glass seal, this shoulder being located so as to seat against the washer 1I when the nut 11 has been screwed on far enough to drawthe copper disc firmly against the embossed ring 15,

: a slight deflection of the copper disc after the pressing thereof firmly against the embossed ring serving to permit the shoulder Il to engage insulating washer 1I.

'Ihe interior of the metal bellows is preferably gold plated and the back electrode'may be of` brass, gold plated, or may beof carbon. The inside of the metal bellows is filled full of granular carbon constantly shaken during the filling process so that no void spaces will be left when the unit is completely assembled. The entire inner surface of the bellows acts as an electrode and therefore need not be provided with an insulating coating although, if desired, insulation in the form of varnish enamel or the like may be provided for the inside of the convolutions of the bellows leaving only the dome shaped top portion to act as a front electrode. The seal disc 14 is use of a very thin mica washer as indicated by reference numeral 8l. Because of the fact that the use of insulation is largely avoided and s ubstantially the entire. bellows is used as an elec- [I .lil

the device constructed as shown in Fig. 9 is high.

While in many instances it may be desirable to have the housing llill solidV so as completely to enclose the resistance unit, additional cooling eiect can be obtained by having openings in the housing 50 or by making this housing in the form of a spider having a plurality of radiating 'arms which extend to the rim which holds the cap I8. In Fig. 9, as in Fig. 6, the diaphragm, which may be of anodic aluminum, bakelized silk or other resilient material of small inertia, is pressed against the end of the metal bellows by action of the cap I8, but is otherwise unsupported. However,` any conventional method of holding the diaphragm in position might be used. With'. the device of Fig. 9, an expansion 'chamber such as disclosed in connection `with Fig. 6, might also be used if desired.

The invention hasbeen particularly described as applied to a telephone transmitter but it will be obvious that the general features of construction are useful in other fields and that a variable resistance element of the general type'described may be used in many different ways. This moisture proof variable resistance element is, for example, adapted for use in electro-mechanical repeaters, and likewise in hearing aids such ,as audiophones. It is also well adapted forincorporation in various kinds of recording instruments wherein a change of condition is indicated by a change of pressure, such for example, as depth gauges, altimeters and barometers, for sound detection under water or in the air and for temperature recording. In the latter instance the pressure may be suppliedv by means of an external force, e. g. a bimetallic spring or the metal bellows itself may be made bimetallic so that it will distort under variation'in temperature, or the air within the metallic chamber may be relied upon to vary the pressure to which the carbon granules are subjected, an increase in temperature resulting in an expansion of the air and a reduction of the pressure on the carbon granules, which follows from an increase in the spacing between the pressure element of the device. Alternatively, in place of air the bellows may be filled with some other form-of expansible gas which is responsive to temperature changes.

While I have described particular embodiments of my invention for purposes of illustration, it.

should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

What is claimed is':

1. A telephone transmitter comprising a housing of insulating material, a resistance unit centrally disposed therein, comprising a' metal bellows serving as an enclosure for said unit and electrically in contact therewith, a metallic diaphragm supported by said housing and arranged to exert pressure against said unit, and -means for trode surface, the current carrying capacity of predetermined position with said one end adja- I cent said housing, means for applying a variable pressure to the other end of said bellows to vary the resistance of said element, and a second contact member xed to said housing of insulated material and disposed to make contact with said metal bellows when the latter is supported in said predetermined position.

4. A telephone transmitter according to claim 3 wherein said post ls screw-threaded in said aperture.

5. A variable resistance element comprising a metal bellows, an electrode within said bellows and electrically insulated therefrom, carbon granules within said bellows, means for insulating the inner side walls of said bellows from said carbon and an expansion chamber connected to said bellows.

6. A 'telephone transmitter comprising a metal bellows containing an electrode and granular carbon, an air-tight moisture proof seal for said bellows and an expansion chamber connected to said bellows.

7. A telephone transmitter comprising a first metal bellows containing granular carbon and having an electrode at each end thereof, one of said electrodes being insulated from said bellows and fixed thereto by means of an air-tight moisture prooi seal, and the other oi-said electrodes being perforated anda second metal bellows fixed to said first metal bellows at the end adjacent said other electrode, saidsecond bellows being weaker than said iirstbellows and serving as an expansion chamber.

8. A telephone transmitter comprising .a chamber having a bellows-like portion of -thin elastic metal and having an aperture in one end, granular carbon inside of said chamber, an electrode within said chamber, a molded insulating member having a metallic insert imbedded therein and extending therethrough, means forming an airtight, moisture-prooi sealbetween said member and said chamber i'or sealing said chamber from the atmosphere, and means connecting saidinsert to said electrode to provide electrical access to said electrode.

9. A telephone transmitter comprising a chamber having a bellows-like portion of thin elastic metal and having an aperture in one end, granular carbon inside of said chamber, an electrode having an enlarged head within said chamber and a shank extending through said aperture, insulatingwashers on said shankinside and outside said chamber, a nut on said shank for tightlyclamping said washers against said chamber and said electrode to rigidly ilx said electrode to said chamber and form an insulating granule-tight seal between said'chamber and said electrode, a molded insulating member having a metallic insert imbedded therein and extending therethrough, means including said member for form-l ing an air-tight additional insulating seal between said chamber andsaid electrode, and means connecting said insert to said shank to provide electrical acsess to said electrode.

E RNIBTB. McLARN. 

